For the first time ever, Music Hack Day came to Denver. The event showcased the underappreciated developer community living in Denver and Boulder, Colorado. The presentations featured several live performances with instruments built during the event. Here are the projects that used the Rdio API:

Sonic Skyline — Source
Select a city and listen to the hottest tracks from the biggest artists. The city's genre is computed from the list of genres of those tracks. Winner, best use of the Rdio API.

ConcertVibe — Website
Browse an interactive tour map for your favorite band. Select any of the concerts and see what people are saying about it on Twitter or listen to the setlist

New Release Roulette — Screenshot
Rebecca
Easily select random tracks from new releases on Rdio. Fine tune the selected tracks by using data from The Echo Nest such as mood, energy, and danceability. The selected tracks are then added to your Rdio queue.

Dream Player — Screenshot
Do Android's dream? This Rdio screensaver for Android displays the artwork for the currently playing tack. The artwork pulses to the music.

Rdio Comment Analysis — Source
Can't decide what if you should listen to an album? Don't want to read all of the comments? This application uses the AlchemyAPI to analyze the sentiment of comments of albums on Rdio. Gives you the overall sentiment and the sentiment of specific tracks.

State of the Game — Website
Tetris where each level gets a song with a faster tempo. Uses The Echo Nest's dynamic playlists.

Rdio is a social jukebox with over 20 million songs to discover, play, and share. Play what you want, when you want, or turn on a station for a perfect mix of songs. Listen anywhere — the web, your phone, even offline — and follow friends and artists to see what they’re playing.

Build millions of songs into your application with the Rdio API. Get started quickly with our Web Playback API, iOS SDK or Android SDK.